The invention is based on the priority patent applications EP 09173733.8 and EP 10165508.2 which are hereby incorporated by reference.
1. Field of the Invention
The invention is related to a process to apply heater function to a plastic glass that is made of a polycarbonate.
More especially the invention is related to a sputtering process that allows to produce high performance heater function on a plastic glass.
Another aspect of the invention is the plastic glass mirror produced by the inventive process.
2. Description of the Related Art
Plastic glass is known in prior art to replace normal silica glasses. For example in EP1412158 a method is disclosed that allows producing plastic glass in a high quality. Typical plastics include optical grade injection mouldable material, optical grade polycarbonates, methacrylates or methacrylate modified polycarbonates. Suitable materials are obtainable from General Electric, for instance, plastics sold under the trade designations MAKROLON 2207 and LEXAN LS2 are particularly suitable in processes. Also, it is necessary to provide optical quality polished mould surfaces to maintain the optical properties of the finished part.
For heating of rear view minors several methods are used.
In the EP 0677434 a solution is proposed that heats the mirror with a resistive metal layer. This layer is sputtered on the minor glass and contacted by electrodes separated by isolating layer in between. The electrodes are connected at one side of the minor, a solution that uses a two-way connector for the power supply of the circuit and thus eases the associated electric bundle.
The use of a restive layer and additional electrodes arises some problems with a harmonious defrosting function. Hot spots occur and can destroy the heating layer.
In U.S. Pat. No. 4,721,550 a printed circuit board is layered by a copper layer. The patent discloses a method to create a very adhesive copper layer on a substrate with a crystalline structure achieved in a porous surface of the polymer substrate.
The deposition of layers with Physical Vapor Deposition (PVD) methods is well known. One successful method is magnetron sputtering.
Magnetron sputtering is a powerful and flexible technique which can be used to coat virtually any work piece with a wide range of materials. Sputtering is the removal of atomised material from a solid due to energetic bombardment of its surface layers by ions or neutral particles. Prior to the sputtering procedure a vacuum of less than one ten millionth of an atmosphere must be achieved. From this point a closely controlled flow of an inert gas such as argon is introduced. This raises the pressure to the minimum needed to operate the magnetrons, although it is still only a few ten thousandth of atmospheric pressure.
When power is supplied to a magnetron a negative voltage of typically −300V or more is applied to the target. This negative voltage attracts positive ions to the target surface at speed. Generally when a positive ion collides with atoms at the surface of a solid an energy transfer occurs. If the energy transferred to a lattice site is greater than the binding energy, primary recoil atoms can be created which can collide with other atoms and distribute their energy via collision cascades.
Aside from sputtering the second important process is the emission of secondary electrons from the target surface. These secondary electrons enable the glow discharge to be sustained.
It is the intention of the invention to overcome the problems of a heater using a resistance layer and separate electrodes and to provide a method using PVD Magnetron process to apply a single layer with a double function to heat and to contact the plastic glass mirror.